Jia Zhen Zheng

Localized oxide degradation in ultrathin gate dielectric and its statistical analysis

Conventional oxide reliability studies determine oxide lifetime by measuring the time to breakdown or quasi-breakdown (QB). In ultrathin gate oxides with T/sub ox/<14 /spl Aring/, however, it is hard to observe breakdown or QB under typical stress conditions. Instead, the gate leakage current shows a continuous increase over the entire time period of electrical stress. As the magnitude of the gate current density increase eventually becomes too high to be acceptable for normal device operation, a lifetime criterion based on the increase in gate leakage current is proposed. Our paper also shows that the area-dependence of the gate leakage current density increase in 13.4 /spl Aring/ oxides is different from that in thicker oxide films, indicating a localized and discrete property of the leakage current. It has also been observed that the oxide lifetime based on the new lifetime criterion is shorter when the gate area is smaller, as opposed to the conventional area dependence of time-to-breakdown test. A simple model consisting of multiple degraded spots is proposed and it has been shown that localized gate leakage current can be described by Weibulls statistics for multiple degraded spots.

Comparison of spin-on materials in IMD planarization

This paper describes the characterization of an etchback process for the new AlliedSignals Accuspin 418 and Hitachi Chemicals HSG R7-13 low dielectric constant silsesquioxane spin-on polymers and the application to the inter-metal dielectric scheme of a 0.35 micrometers device. A comparison with a conventional polysiloxane spin-on glass (AlliedSignals Accuglass 214) is also briefly discussed. The predominant factor affecting the selectivity of PECVD oxide to spin-on polymer is the CHF3CF4 flow. A low selectivity in which the spin-on polymer etches faster was found to rid of spin-on polymer on top of large metal features where vias may be cut while simultaneously leaving behind sufficient oxide on top of metal lines and the spin-on polymer in the metal spaces. After etchback, a thick PECVD oxide is deposited and planarized by chemical mechanical polishing.